1. Field of the Invention
The present invention relates to an apparatus and method for scrambling video data, and more particularly, to a scrambling apparatus and method using conversion of motion vector information of video data.
2. Description of the Related Art
When a cable broadcasting station broadcasts a certain program through a pay-per-view channel, video data such as movies and TV programs sometimes must be scrambled to allow only regular subscribers to watch.
For a viewer who has received scrambled video data to view the video, the viewer must have a descrambler to descramble the received video data, and if the viewer tries to view the video without descrambling the scrambled video data, the viewer cannot view the video.
Since a conventional scrambling apparatus totally scrambles video data so that nobody but regular subscribers can view the video, it is impossible for cable broadcasting stations to allow general users (not regular subscribers) to partially watch the video, so they might lose the chance to make more contracts with general users and the apparatus also causes complexity of calculation and decrease of a processing speed.
To solve these problems, for example, Japanese patent publication No. JP 6-90451 ‘SCRAMBLING APPARATUS’ discloses a method of scrambling video data by converting motion vector codes of compression data of the video data based on an H.261 or MPEG standard into other motion vector codes indicating the same code lengths as and different values from the original motion vector codes.
However, since a conversion range between motion vector codes indicating the same code lengths as and different values from each other is narrow, a scrambling effect decreases, and furthermore, if conversion of motion vector codes is performed for every input macroblock, security becomes weak due to regularity of the conversion.